Electrical instrument



March 13, 1945.

Maz E, Ken/N6, leV

Patented Mar. 13, 1945 UNITEE STATES PATENT' FFI Iarrasar: l

EmcraroAnms'mUMsNr Jack n. Keeling. Jr., college station, 'ren Application May 24, 194i, serai No. 39am z claims. (ci. irs-'183) This invention relates to an electrical instrument. v

An object of the invention is to provide a circuit having an alternating current constant that requires very little energy'to change the constant and to measure minute changes in said constant whereby the circuit is applicable to practically every measurement involving dimensions or dimensional charges, electrical constants or changes in electrical constants where precision is important.

Another object is to provide a novel means for measuring linear displacements to an accuracy of better than one millionth of an inch.

With the above and other objects in view the invention has particular relation to certain novel features of construction, operation and arrangements of parts, an example of which is given in this specification and illustrated in the accompanying drawing, wherein:

Figure 1 shows' a circuit diagram of the instrument.

Figure 2 shows a vector diagram of the circuit at balanced condition.

Figure 3 shows a vector diagram ofthe circuit at slightly unbalanced condition.

Referring now more particularly to the draw- I component of the xed resonant branch, prefer-v ed to minimize electrostatic coupling of this coil and other portions lof the circuit by means of electrostatic shield 5. Magnetic coupling is the more desirable method of transferring electrical energy to coils 2 and 3.- The coils 2 and 3 are as nearly identical in electrical characteristics as A Il and trimmer 'condenser I2. The coil 2, condenser I and trimmer Il forms onevariable branch and the coil I, condenser Il andtrimmer I2 form the other variable branch. Coil Il and condenser l5 form a resonant series branch which is independent of the variable branches.

Therefore. between junctions I and I3 exist the It the circuit is balanced.k Condensers 9 and ll have a common moving element and likewise the trimmers l0 and l2 have a common moving ele" ment.

A voltage detector I6 is connected across a ably condenser l5. In conjunction with voltage dectector l5 is an indicator il which indicates the energy in the fixed branch.

The voltages and currents are indicated by arrows in Figure 1 and vectors in Figures 2 and` 3. The electromotive forces E-2 and E-B induced in the coils 2 and t are .shown at 8 and 'l respectively. The currentsI-2, 1 3, I-lt in electromotive forces induced therein as a ,result of the current in coil 4. In the balanced condition the two variable branches of the circuit (with coil 2 and coil 3 as components) are identical. In this balanced state there exists no potential difference between Junctions a and i3 and none of the energy delivered to' the circuit is present in the center branch comprising coil I4 and condenser l5. The' current vI-l and voltage V--l are zero for the balanced condition. When the moving element of condensers 9 and II is displaced from the position of electrical balance, one condenser increases incapacity While the other decreases. The balance is thus upset and there develops a potential difference' between Junctions 8 and I3. CurrentI-M and voltage V-I5 arise from the electrically unbalance condition. The magnitude of the current I-'|4 is comparatively large for a givendisplacement because the middle branch has a minimum impedance. The voltage V--IB across the condenser is many times greater than the voltageacross the entire branch because of resonance; therefore, a relatively large voltage V-I' results from a minute displacement from the balance position. The use. of the resonant circuit for the middle branch increases the sensitivity about a thousand fold in practice. Voltage detector I6 and 'indicator Il respond to the voltage VI5. The moving element. of the trimmer condensers I0 and l2 is then displacedin such a direction to offset the displacement of the moving element of condensers 9 and Il. The amount oi' displacement required of the trimmer condensers moving coils 2, 3 and M respectivelyare shown at Writ,

'element is proportional to the displacement of the moving element of the condensers I and Il for small displacement. Thus by evaluating the displacement of the trimmer condensers in and Il required to restore balance, the displacement ,producing unbalance is known. The null methodoi. measuring is unnecessary when the voltage V-I is evaluated suitably by the indicator I1.

In all the circuits hereinbeiore explained, it will be noted that each circuit is composed -of bilateral impedances, the energy source and the energy receiver, or indicator may be interchanged.

being connected in parallel, one of said branchesy being xed and the other branches being adjustable, a generator coupled inductively to the two adjustable branches in a manner to excite each equally with an alternating current oi' the resonant frequency of the unexcited xed branch, the excited adiustable branches having a double capacitor with an electrically common plate that increases one capacitance while decreasing the other capacitance as a result oi a displacement oi the electrically common plate, a volt meter connected to meter the voltage developed across a reactive member in the iixed branch which is proportional to the displacement of the electrically common plate for very small displacements.

2. A device of the character described comprising three approximately resonant series branches, each branch being composed of capacitative and inductive reactors, said branches being connected in parallel, one of said branches being ilxed and thepther branches being ad-l justable, a generator coupled inductively to the two adjustable branches in a manner to excite each equally with an alternating current of the resonant frequency of the unexcited ilxed branch, the excited adjustable branches having a double capacitor with an electrically common plate that increases one capacitance while decreasing the other capacitance as a result of a displacement o! the common plate, a voltmeter connected to meter the voltage developed across a reactive member in the fixed branch that results from the movement of the cmnmon capacitator plate from 4 the equaleapacity position, an 'auxiliary twin capacitator connectedA in parallel with the rst mentioned twin capacit-or which can be manually adjusted by displacing. its common plate to compensate for the displacement of the common plate of the first mentioned twin capacitor in order to use the volt meter as an indicator of 3 exact compensation.

JACK R. KEELING, Ja. 

